Prior art documents related to conventional power supply devices for electrical discharge machines include Patent Literatures 1 and 2 described below.
In the power supply device for an electrical discharge machine described in Patent Literature 1, a technology is disclosed in which switching elements, which intermittently generate a pulse train having a predetermined repetition frequency every predetermined time, are driven and an AC pulse current is supplied to the machining gap between the machining electrode and a workpiece, with a capacitor connected in parallel, thereby preventing a follow current of an arc current by completely discharging the charge in the capacitor to the machining gap and thus improving the surface roughness in the electrical discharge machining.
Moreover, in the power supply device for an electrical discharge machine described in Patent Literature 2, a technology is disclosed in which, in the configuration that includes a DC power supply for supplying a DC pulse current to the machining gap between the machining electrode and a workpiece, a series circuit composed of a switching element and a resistor, a capacitor that is connected in parallel with the machining electrode and the workpiece, and a discharge detecting unit that detects the occurrence of a discharge in the machining gap, an on/off control to turn on the switching element for a pulse width that is equal to or less than the pulse width of a discharge current of the capacitor and to turn off the switching element for a predetermined time is repeated until the capacitor discharges and the discharge detecting unit detects the discharge and the on/off control is repeated again after a predetermined off-time after detection of the discharge by the discharge detecting unit. According to the power supply device for an electrical discharge machine described in Patent Literature 2, a follow current of an arc current is prevented in a similar manner to Patent Literature 1 by preventing a current having a pulse width equal to or larger than the pulse width of the discharge of the capacitor from flowing in the gap (hereinafter, referred to as “machining gap”) between the machining electrode and a workpiece (see FIG. 2 and FIG. 11).